Abstract
Chemical and electronic properties of scrapecleaned YBa2Cu3O7−δ(YBCO) ceramics, which were also annealed in vacuum or exposed to H atoms or O2 molecules, were studied at room temperature by applying Auger electron (AES) and low-energy electron energy-loss spectroscopy (LEELS). Scanning electron micrographs showed such scraped surfaces to consist mainly of small, fractured YBCO crystallites, i.e. of clean YBCO surfaces. With only one exception, all low-energy AES lines were found to be shifted in energy compared to data recorded with surfaces of metallic Cu and Y. The analysis of the high-energy AES lines indicated the existence of non-stoichiometric material in grain boundaries. At least 25 different LEELS features were recorded. The 24.9-eV energy loss, which is due to the excitation of bulk valence-electron plasmons, indicates an enhanced oxygen deficit δs ≈ 0.8 at scrape-cleaned YBCO surfaces. Annealing of scraped YBCO samples at approximately 700 K in vacuum and also their exposure to hydrogen atoms resulted in an additional oxygen depletion within a few atomic layers near to the surfaces. These oxygen deficiencies were found to increase the intensity ratios of low-and high-energy AES lines of Cu, Ba, and Y and to intensify the energy-loss peak at 4.4 eV which has been attributed to O−Cu−O dumbbells.
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Hockertz, J., Clemens, H.J. & Mönch, W. Surface studies on polycrystalline YBa2Cu3O7−δ with Auger electron and low-energy electron energy-loss spectroscopy. Z. Physik B - Condensed Matter 90, 331–339 (1993). https://doi.org/10.1007/BF01433057
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DOI: https://doi.org/10.1007/BF01433057